DAVOS, Switzerland (AP) — The head of the U.N.'s World Food Program is telling billionaires it's "time to step up" as the global threat of food insecurity rises with Russia's war in Ukraine, saying he's seen encouraging signs from some of the world's richest people, like Elon Musk and Jeff Bezos.

Agency Executive Director David Beasley built upon a social media back-and-forth he had with Musk last year, when the Tesla CEO challenged policy advocates to show how a $6 billion donation sought by the U.N. agency could solve world hunger.

Since then, "Musk put $6 billion into a foundation. But everybody thought it came to us, but we ain't gotten any of it yet. So I'm hopeful," Beasley told The Associated Press at the World Economic Forum in Davos, Switzerland, where some of the world's biggest elites and billionaires have gathered.

"I don't know what it's going to take," he said of Musk. "We're trying every angle, you know: Elon, we need your help, brother."

Musk and Bezos didn't immediately respond to emails or other messages seeking comment.

Musk, the world's richest man, donated about 5 million shares of company stock worth roughly $5.7 billion to an unidentified charity in November, according to a regulatory filing.

It came after Musk tweeted in late October that he would sell $6 billion in Tesla stock and give the money to the World Food Program if the organization would describe how the money would solve world hunger. The U.S. Securities and Exchange Commission filing did not name any recipients for Musk's donation.

Beasley told AP on Monday that his message wasn't just to those two high-profile tech mavens, but other billionaires, too.

"The world is in real serious trouble. This is not rhetoric and B.S. Step up now, because the world needs you," he said.

Ukraine and Russia together export a third of the world's wheat and barley and half of its sunflower oil, while Russia is a top supplier of fertilizer that has surged in price. The Kremlin's forces are accused of blocking Ukrainian ports, and the interruption of those affordable food staples is threatening food shortages and political unrest in countries in Africa, the Middle East and Asia.

The threat to the global food supply has been a pressing concern for officials, with U.N. Secretary-General Antonio Guterres saying last week that he was in "intense contacts" with Russia and other key countries and is "hopeful" of an agreement to allow the export of grain stored in Ukrainian ports and ensure Russian food and fertilizer have unrestricted access to global markets.

If Ukraine's supplies remain off the market, the world could face a food availability problem in the next 10 to 12 months, and "that is going to be hell on earth," Beasley said.